Cast metal engine blocks for a multi-cylinder, in-line, two-cycle engine generally consist of a cylinder block and three separate cast covers, including two water passage covers and an exhaust passage cover, all of which are attached to the cylinder block by bolts. To provide the connection between the covers and the cylinder block, the cylinder block is formed with a series of enlarged lands or bosses, which are drilled or cast and tapped to receive bolts, and similarly mating holes are drilled or cast in the covers. In addition, the mating surfaces between the covers and the cylinder block are machined and the covers are attached to the cylinder block through gaskets and bolts. The gasketed surfaces must be provided with a substantial width to receive the gaskets and prevent leakage between the components.
In the fabrication of a conventional three-cylinder, two-cycle engine, as many as 100 fasteners, such as bolts, screws, and the like, are required to attach the covers to the cylinder block and substantial time and labor is required in machining the interfaces, tapping and drilling holes, applying gaskets and bolting the covers to the block. The intensive labor that is required is a substantial factor in the overall cost of the engine.
Furthermore, the requirement for providing bosses on the cylinder block and the increased width of the gasket surfaces adds to the overall weight of the engine.
In evaporable foam casting processes, a pattern is formed of an evaporable foam material, such as polystyrene. The foam pattern is substantially identical in configuration to the cast metal part to be produced, subject to shrinkage and/or other conditions of the casting process. The foam pattern is placed in a mold and surrounded with a finely divided medium, such as sand, which also fills the cavities in the pattern. When molten metal is introduced into the mold, the molten metal will heat and vaporize the pattern, with the vapor passing into the interstices of the sand, while the molten metal will fill the voids created by vaporization of the foam to provide a cast metal part having substantially the same configuration as the foam pattern. Evaporable foam casting processes have particular advantage when casting parts of unusual or complex contours.